The Internet Engineering Task Force (IETF) is working on standardization of Bidirectional Forwarding Detection (BFD) as a protocol, independent of the routing protocol, for detecting communication failure between node devices and on the next hop. BFD regularly transmits and receives packets between systems by using the User Datagram Protocol (UDP) and, when no packet is received for a certain length of time, it is assumed that some failure has occurred on the communication path (failure on the route). This length of time is predetermined, and will hereinafter be referred to as detection time. The detection time is calculated from the interval at which packets are transmitted and a detection multiplier which represents the minimum number of packets consecutively lost to make the losses regarded as a failure, and the equation by which it is figured is stated to be “the transmission interval×the detection multiplier” is prescribed in Bidirectional Forwarding Detection, draft-ietf-bfd-base-05,June, 2006 for instance.